Summary of Work: DNA damage produces cell death or mutation, both of which can have serious health consequences. Most DNA damage is repaired before it can cause harm. The classically defined mechanisms of repair are direct reversal of the damage, excision of the damage followed by resynthesis of the damaged strand, recombinational processes that bypass the damage without removing it, and mutagenic translesion synthesis. A fourth but poorly characterized mechanism has been identified in bacteriophage T4. Mutations in genes of DNA replication reduce survival after treatments inducing a variety of kinds of damage, but do not otherwise appreciably affect phage reproduction. The process appears not to involve any of the classical mechanisms. We will investigate the processing of damaged DNA in vitro using wild-type and mutant enzymes, and will seek additional mutations in the epistasis group.